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We apply the mirror principle of [L-L-Y] to reconstruct the Euler data $Q=\{Q_d\}_{d \in{\tinyBbb N}\cup\{0\}}$ associated to a vector bundle V on ${\smallBbb C}{\rm P}^n$ and a multiplicative class b . This gives a direct way to compute the intersection number $K_d$ without referring to any other Euler data linked to $Q$ . Here $K_d$ is the integral of the cohomology class $b(V_d )$ of the induced bundle $V_d$ on a stable map moduli space. A package '{\tt \verb+EulerData_MP.m+}' in Maple V that carries out the actual computation is provided. For b the Chern polynomial, the computation of $K_1$ for the bundle $V=T_{\ast}{\smallBbb C}{\rm P}^2$, and $K_d, d=1,2,3$, for the bundles ${\cal O}_{{\tinyBbb C}{\rm P}^4}(l)$ with 6≤l≤10 done using the code are also included.

This is a continuation of "Mirror Principle III"(math.AG/9912038).

The computations that are suggested by String Theory in the B model requires the existence of degenerations of CY manifolds with maximum unipotent monodromy. In String Theory such a point in the moduli space is called a large radius limit (or large complex structure limit). In this paper we are going to construct one parameter families of n dimensional Calabi-Yau manifolds, which are complete intersections in toric varieties and which have a monodromy operator $T$ such that $(T^N − id)^{n+1} =0 $ but $(T^N −id)^n \ne 0$, i.e the monodromy operator is maximal unipotent.

This note briefly reviews the {\it Mirror Principle} as developed in the series of papers \LLYI\LLYII\LLYIII\LLYIV\LCHY. We illustrate this theory with a few new examples. One of them gives an intriguing connection to a problem of counting holomorphic disks and annuli. This note has been submitted for the proceedings of the Workshop on Strings, Duality and Geometry the C.R.M. in Montreal of March 2000.